EKG and high-sensitivity troponin T may rule out myocardial infarction

Among chest-pain patients with no new ischemia on an electrocardiogram (EKG) and troponin
T below 0.005 µg/L, only 0.5% had an acute myocardial infarction during hospitalization
and none died.

A single measurement of high-sensitivity cardiac troponin T and an electrocardiogram
(EKG) may rule out acute myocardial infarction (AMI) in ED patients, according to
new meta-analysis.

Researchers included 11 cohort studies with 9,241 patients who presented to the ED
with possible acute coronary syndrome and received an EKG and measurement of high-sensitivity
cardiac troponin T. The primary outcome was AMI during hospitalization and secondary
outcomes were major adverse cardiac events (MACE) or death within 30 days. Results were published in the April 18 Annals of Internal Medicine.

Patients were classified as low risk if they had no new ischemia on EKG and the troponin
measurement was below 0.005 µg/L; 30.6% of the study patients fell into this
category. An AMI occurred during hospitalization in 0.5% of these patients. Sensitivity
of the risk classification for AMI ranged from 87.5% to 100% in the studies, with
a pooled estimate of 98.7% (95% CI, 96.6% to 99.5%). None of the low-risk patients
died and sensitivity for MACE within 30 days ranged from 87.9% to 100% in the studies,
with a pooled sensitivity of 98.0% (95% CI, 94.7% to 99.3%).

“Integrating such an early screening approach into existing investigative strategies
may enable patients to be safely discharged to outpatient follow-up earlier than in
current practice,” the authors said. However, they noted several caveats, including
that the rule-out strategy showed much lower sensitivity in two of the included study
cohorts than in the others, “which could indicate that the strategy is not
universally safe.”

It's also known that troponin may not be detectable immediately after myocardial injury,
so this strategy would not be recommended for patients presenting within three hours
of symptom onset, the authors said. The results also only apply to the studied assay,
not any future troponin T assays. The specificity of this strategy is low, so it should
not be used to rule in AMI or to identify patients at high risk.

Future research should combine this rule-out strategy with assessment of risk factors
and symptoms, the authors suggested. “The incorporation of risk and symptoms
may reassure physicians of the safety of the early rule-out strategy, although possibly
at the risk of lower efficacy,” they wrote. Hospitals that decide to implement
the rule-out strategy should also conduct local audits to ensure safety and efficacy,
they advised.

ACP Hospitalist provides news and information for hospitalists, covering the major issues in the field. All published material, which is covered by copyright, represents the views of the contributor and does not reflect the opinion of the American College of Physicians or any other institution unless clearly stated.